Flow rate detection device

Abstract

A flow rate detection device of the invention comprises a flow rate meter 11 for outputting an output value Vd depending on a gas flow rate and detects the gas flow rate by calculating the gas flow rate on the basis of the output value output from the flow rate meter. In this invention, it is judged if the output value output from the flow rate meter should be corrected on the basis of the flow rate of the gas passing through the flow rate meter and its change rate. When it is judged that the output value output from the flow rate meter should be corrected, the output value output from the flow rate meter is corrected and then, the gas flow rate is calculated on the basis of this corrected output value.

The invention claimed is: 
     
       1. A flow rate detection device comprising a flow rate meter for outputting an output value, depending on a flow rate of a gas, the device detecting the gas flow rate by calculating the gas flow rate on the basis of the output value output from the flow rate meter,
 wherein it is judged if the output value output from the flow rate meter should be corrected on the basis of the flow rate of the gas passing through the flow rate meter and the change rate of the flow rate and when it is judged that the output value output from the flow rate meter should be corrected, the output value output from the flow rate meter is corrected and then, the gas flow rate is calculated on the basis of the corrected output value, 
 wherein it is judged if the condition of the gas passing through the flow rate meter has changed from the laminar condition to the turbulent condition or vice versa or the flow direction of the gas passing through the flow rate meter has inverted and then, when it is judged that the condition of the gas passing through the flow rate meter has changed from the laminar condition to the turbulent condition or vice versa or the flow direction of the gas passing through the flow rate meter has inverted, it is judged that the output value output from the flow rate meter should be corrected, 
 wherein a point defined by the flow rate of the gas passing through the flow rate meter and its increase rate when the condition of the gas passing through the flow rate meter has changed from the laminar condition to the turbulent condition is previously obtained as a flow rate increase condition transition point and a point defined by the flow rate of the gas passing through the flow rate meter and its decrease rate when the condition of the gas passing through the flow rate meter is previously obtained as a flow rate decrease transition point, 
 wherein when the flow rate of the gas passing through the flow rate meter, it is judged if the point defined by the flow rate and its increase rate is the flow rate increase condition transition point and when it is judged that the point defined by the flow rate of the gas passing through the flow rate meter and its increase rate is the flow rate increase condition transition point, it is judged that the condition of the gas passing through the flow rate meter has changed from the laminar condition to the turbulent condition, and 
 wherein when the flow rate of the gas passing through the flow rate meter decreases, it is judged if the point defined by the flow rate and its decrease rate is the flow rate decrease condition transition point and when the point defined by the flow rate of the gas passing through the flow rate meter and its decrease rate is the flow rate decrease condition transition point, it is judged that the condition of the gas passing through the flow rate meter has changed from the turbulent condition to the laminar condition. 
 
     
     
       2. The device as set forth in  claim 1 , wherein a relationship between the output value output from the flow rate meter and the current gas flow rate when the change rate of the gas flow rate is zero or generally zero is previously obtained, and
 wherein the gas flow rate is calculated from the previously obtained relationship on the basis of the output value output from the flow rate meter or the corrected output value. 
 
     
     
       3. The device as set forth in  claim 1 , wherein the correction degree of the output value output from the flow rate meter when the output value is corrected is determined, depending on at least one of the flow rate of the gas passing through the flow rate meter and the change rate of the flow rate. 
     
     
       4. The device as set forth in  claim 1 , wherein the first order lag is eliminated from the output value output from the flow rate meter before the output value is corrected, the output value after its first order lag is eliminated, is corrected when it is judged that the output value output from the flow rate meter should be corrected, and the gas flow rate is calculated on the basis of the corrected output value. 
     
     
       5. The device as set forth in  claim 1 , wherein the flow rate meter is a silicon chip type flow rate meter. 
     
     
       6. The device as set forth in  claim 1 , wherein the flow rate meter has a heating resistor which generates a heat by the application of the electric voltage to the resistor,
 wherein the electric voltage is applied to the resistor, depending on the heat amount removed from the resistor by the gas passing through the flow rate meter, and 
 wherein the output value is output, depending on the heat amount removed from the resistor by the gas passing through the flow rate meter.